Implement GL_OES_surfaceless_context BUG=angleproject:1651 Change-Id: I733ccedad7c7424cdb70e21ef8d48b2a15ccdfd7 Reviewed-on: https://chromium-review.googlesource.com/434762 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>